Wood pulp making



July 14, 1936. PA APAULSON 2,047,488

wooD PULP MAKING Filed May 2l, 1954 BLOWER fil Patented July 14,/ 1936 l PATENT OFFICE 2,047,488 woon mr Mama Peter A. Paulson, Appleton, Wis.

Application May 2l, 1934, Serial No. 726,646

' 1o calm. (ci. :az-11) This invention relates to anv improved method of and apparatus for producing wood pulp for paper making, and especially to an improved sulphfte process of producing wood pulp for paper .making and to appar'atus for carrying on the process.

The main -ob'iects of the invention are to provide a commercially practicable continuous process for producing wood pulp; to provide such a process which may be practiced with apparatuswhich may be easilyproduced or obtained and set up; to provide a process which will be efcient and economical in operation `and which may be carried on in a more or less'automatic manner; to provide simple but eillcient apparatus for carrying on the process; and in general, it is the object of this invention to provide an im provement in the art of wood pulp making.

Other objects and advantages. of the invention will be vunderstood by reference to .the following specication and accompanying drawing in which there is illustrated one selected form of apparatus for commercially producing theinvention.

Referring now to the drawing, there is illustrated a receptacle or digester designated 5, which is preferably in'the'form of a vertically disposed elongated tank made of crome nickel alloy steel or of other suitable material which will satisfactorily resist the corrosive effect of the acids introduced and formed in the receptacle during the production of wood pulp.

They upper end of the digester is ofconical shape and is connected to a conveyor S-of any suitable type which `feeds chips to the digestcr from a supply hopper designated 1. The conveyor 8 may be a screw conveyor or any other suitable type which will serve to convey chips from the supply hopper to the digester.

A pipe connection 8 communicating with the interior of the digester is providedfor introducing into the digester liquid containing the base, for example lime and magnesia or the equivalent which is used in the process.

'Ihe bottom of the digester is also of conical form and a series of ports designated 9 are provided in circumferential spaced relation around the digester.

through a `manifold III which communicates with theports 9 and pipe line il which communicates manifold 2Q surrounding the digester near its dis- These ports serve to permitthe introduction of the desired hot gases and steam for eifecting' the cooking. 'I'he ports 9 being spacedcess'gases rising from the mixture in the digester with a separating tank I2 wherein the hot gas and steam are produced.

The chips, base-liquid, gas and steam are supplied continuously in proper proportions and pulp is accordingly produced in a continuous manner. 5

, 'I'he finished pulp is discharged from thelower end of the receptacle or digester and passed through a pipe line I3 to a level co'ntrol tank I4 which is provided with a dam indicated at I5. Material ilowing over the dam will pass .out oi the level maintaining device I4 through a pipe connection IG into a illter or strainer Il. The filter or strainer may be of more or less conventional screen drum construction. In the said strainer or filter, the liquid is extracted from the pulp product, the liquid passing-through the screen drums and emerging from the interior of the drums into a pipe line I8. The partially thickened 'pulp which leaves the strainer I1 through the pipe connection I9 next enters a 20 suitable pressl 2li which presses more of the liquidA out of the pulp. The liquor pressed out of the carries the waste liquor to any desired disposal system and the pressed pulp emerges from the 25 mouth 22 of the press and is conveyed to a washer in any suitable manner.

It will be seen that by reason of the dam I5 in the level controlling box I4, a predetermined level will be maintained in the digester over the top of the mixture of chips, liquid and acid.

. The liquid removed from the pulp in the `lter Il is conducted by the pipe line I8 to a pump 23. which feeds the liquid under pressure to a charge end, the manifold supplying the hot liquid to the interior of the digester through a series of ports 25 which are spaced circumferentially around the digester. The introduction of the hot liquid through the ports 25 serves to thin down the pulp iso as to facilitate its passage through the Vpipe line I3 to the level control box I4 and strainer I'I. A portion of the hot liquid fed by the pump 23 is also conveyed by a pipe 26 to a nozzle 21 which enters the pipe line I3 in la position to assist the movement of the thinned pulp through the pipe line I3'.

In the sulphite process of producing wood pulp, an .excess 'of heat and sulphur dioxide gases is normally required to eifect proper cooking. Ex- 50 the mixture. It will be apparent that no pressure is produced in the digester other than that incident to the weight of the column of chips and liquid. This is possible because a constant ow of a mixture of sulphur dioxide and steam is supplied to the digester through the ports 9. Hence, the digester need not be of the usual thick construction. This thinner construction will allow the use of comparatively high grade acidresisting metal, such as previously mentioned without prohibitive expense.

Gas such as sulphur dioxide is supplied through a pipe line 29 from a suitable source of supply to a blower 29' which may be driven by an electric motor as indicated, or otherwise. The gas is conveyed from the blower 29 through a pipe line 30 to an acid absorber 3I which may be of any suitable type, for example, the type commonly used in the milk of lime system, wherein the gas is absorbed in cold water. Cold water is introduced into the upper end of the acid absorber by means of a pipe connection 32. The acidbearing water is drawn out of the absorber by means of a suitable pump designated 33 and discharged into a pipe 34 which communicates with two heat exchangers, onedesignated 35 and the other designated 36. A portion of the acid liquid is thus passed through the heat exchanger 35 and another portion through the heat exchanger 36.

Hot water drained from the separating tank I2 passes through a pipe 3'I into the heat exchanger 35 to pre-heat the cold acid liquid which is supplied to this heat exchanger. The preheated acid liquid is conducted through a pipe 38 from the heat exchanger 35 to another heat exchanger 39. Live steam enters the heat exchanger 39 through the steam inlet pipe 40 and is exhausted from the heat exchanger through the outlet pipe 4I which carries the steam condensate back to the boiler for re-heating. In the heat exchanger 39, the pre-heated acid liquid from the heat exchanger 35 is raised to the desired high temperature and the hot acid liquid is conveyed by a pipe 42 from the heat exchanger 39 to the separating tank. The acid liquid which enters the heat exchanger 36 receives a pre-heating from the hot gases from the vent 28, through a pipe line 43 and the pre-heated acid liquid is conveyed from the heat exchanger 36 through a pipe line 44 to the heat exchanger 39. It will be seen that the pipe lines 38 and 44 are brought together and the entire supply. of acid liquid is introduced to the heat exchanger 39.

In the separating tank I2, the hot acid liquid separates into hot acid gas and steam and hot water. The gas and steam in its heated condition ows throughV the pipe line II into the di-V cooled water is conveyed from the cooler 45 through apipe linev 41 which connects with the cold water pipe line 32 which enters the acid absorber. For effecting cooling in the cooler 45, cold water is used, such cold water entering through the pipe line 48 and being discharged through the pipe 49.

The hot relief gases used for pre-heating the acid liquid in the heat exchanger 36, are con- .ducted from the heat exchanger 36 to a cooling coil 50 in which such relief gases are cooled and from which the cooled gases are conducted by a pipe line 5I to the pipe line 28 which supplies cooled acid gas to the blower 29'. A by-pass pipe line 52 may be provided for eliminating the pre- 5 heating heat exchanger 36 and cooler 50 in the event that it is desired to return the relief gases from the vent 28 directly to the gas supply line 29.

Obviously, other arrangements may be made 10 for pre-heating and heating the acid liquid and for cooling the relief gases and the hot water drawn from the separating tank I2. However, 'the above described arrangement is quite economical and eicient in that it utilizes as far as 15 practicably possible all of the heat developed by the process. while also saving for re-use all of the relief gases and unused acid liquid.

Valves may, of course, be provided in the various pipe lines at desirable points for controlling 20 the flow of uids therethrough. In the foregoing description, the valves have not been speciiically mentioned, but it will be observed that such valves are illustrated in convenient loca- -tions and the effects of closing or opening the 25 valves will, of course, be apparent.

Changes in the described apparatus may be made and the method otherwise carried on without departing from the' spirit of the invention, the scope of which should be determined by 30 reference to the following claims which should be construed as broadly as possible consistent with the state of the art.

I claim:

1. The process of making wood pulp which con- 35 sists in supplying tothe inlet end of an elongated receptacle, a mixture of wood chips and a basecontaining liquid, conducting said mixture through said receptacle, introducing acid gas into said receptacle at a point spaced from the chip inlet, permitting the escape of gases to prevent the development of excessive pressure within the receptacle, discharging the treated material from the other end of the receptacle, propelling cold acid gases to an acid absorber, withdrawing cold acid liquid .from said absorber, heating said acid liquid by passing the same through a heat exchanger, delivering the heated acid to a separator for separating acid gas from said heated acid liquid to provide a Asupply of said' acid gas for introduction into said receptacle, passing hot liquid from said separator through said heat exchanger for heating some of said acid, and introducing the hot liquid after passing through said heat exchanger to said acid absorber.

2. The process of making wood pulp which consists in supplying to the inlet end of an elongated receptacle, a mixture of wood chips and a basecontaining liquid, through said receptacle, introducing acid gas into said receptacle at a point spaced from the chip inlet, permitting the escape of gases to prevent the development of excessive pressure within the receptacle, discharging the treated material from 65 the other end of the receptacle, propelling cold acid gases to an acid absorber, withdrawing cold acid liquid from said absorber, heating said acid liquid by passing the same through a heat exchanger, delivering the heated acid to a separator 70 for separating acid gas from said heated acid liquid to provide a supply of said acid gas for introduction into said receptacle, passing hot liquid from said separator through said heat exchanger for heating some of said acid, introducconducting said mixture 60 Cil ing the hot liquid after passing through said heat exchanger. to said acid absorber, and introducing the escaped gases from said receptacle to said absorber with said cold acid gas.

3. 'I'he process of making wood pulp which consists in supplying to the inletend of an elongated receptacle, a mixture of wood chips and a base-containing liquid, conducting said mixture through said receptacle, introducing acid gas into said receptacle at a point spaced from the chip inlet, permitting the escape of gases to prevent the development of excessive pressure within the receptacle, discharging the treated material from the other end of the receptacle, propelling cold acid gases to an acid absorber, withdrawing cold acid liquid from said absorber, heating said acid liquid by passing the same through a heat exchanger, delivering the heated acid to a separator for separating acid gas from said heated acid liquid to provide a supply of said acid gas for introduction into said receptacle, passing hot liquid from said separator through said heat exchanger for heating some of said acid and ,whereby said hot liquidk is cooled, passing the receptacle, discharging the treated material from the other end of the receptacle, propelling cold acid gases to `an acid absorber, withdrawing cold acid liquid from said absorber, heating said acid liquid by passing the same through a heat veirchanger, delivering the heated acid to a separator for separating acid gas from said heated acid liquid to provide a supply of said acid gas for introduction into said receptacle, passing hot liquid from said separator through said heat exchanger for heating some of said acid and whereby said hot liquid is cooled, passing the cooled liquid through another cooling device so as to render the liquid cold, introducing the cold liquid to said acid absorber, and introducing the relief gases from said receptacle to said absorber with said cold gas.

5. The process of making wood pulpl which consists/ in supplying to the inlet end of an elongated receptacle, a mixture of wood chips and a basecontaining liquid, .conducting said mixture through said receptacle, introducing acid gas into said receptacle at a point spaced fromthe chip inlet, permitting the escape of gases to prevent the development of excessive pressure within the receptacle, discharging the treated material from the other end ofthe receptacle, propelling cold acid gases to an acid absorber, withdrawing cold steam in the digester,

` 3 acid liquid from said absorber, heating said acidv lliquid by passing thesame through a heat exchanger, dellvering the heated acid to a separator for separating acid gas from said heated acid liquid to provide a supply of said acid gas for introduction into said receptacle, passing hot liquid from said separator through .said heat exchanger for heating some of said acid, introducing the hot Aliquid after passing through said heat7 f' liquid when the liquid is passed into a separator.

and injecting the separated gas in the digester.

7. The process pf making wood pulp which comprises the steps of conducting relief gas from a digester and fresh acid gas to an acid, ab-

hot relief -gas from the digester, additionally heating said liquid sufllciently to cause acid gas to separate from the liquid when the liquid is passed intoa separator, and injecting the separated gas in the digester.

8. The process of making wood pulp which comprises the steps of conducting relief gas from a digester and fresh acid. gas to an acid absorber to produce acid liquid.' preheating some of said acid liquid in aheat exchanger by heat from liquor from an acid separator, .additionally heating said lliquid sufficiently to cause acid gas to separate ,from the liquid when the liquid is passed into said separator, and injecting? the separated gas in the digester.

9. Thefprocess of making wood Sorber to produce acid liquid, preheating some of said acid liquid in a heat exchanger by heat from pulp which comprises the steps oi' conducting relif gas from..

a digester and fresh acid gas to an absorber toA produce 'acidliquid, preheating some of said acid liquid in a heat exchanger by heat from hot relief\v gas from the digester, preheating some of saidv 1 acid liquid in a heat exchanger 'by heat from hot liquor from an acid separator, ladditionally 4heating said liquid sufficiently to cause acid gas to separate from the liquid when thelatter is passed into said separator, and injectingJ the separated gas in the digester.

10. The 'process of'making wood pulp which comprises the steps of conducting relief gas from a digester and fresh acid gas to an acid absorber to produce acid liquid, heating said liquid sumcientlyto cause acid gas and steam to ,separate from the liquid when the liquid is passed into a separator, and injecting the separated PE'I'ER A. PAUIaoN.

Sas and 

